This disclosure is generally directed to toner processes, and more specifically, emulsion aggregation and coalescence processes, as well as toner compositions formed by such processes and development processes using such toners.
Emulsion aggregation/coalescence processes for the preparation of toners are well known.
In a number of electrophotographic engines and processes, toner images may be applied to substrates. The toners may then be fused to the substrate by heating the toner with a contact fuser or a non-contact fuser, wherein the transferred heat melts the toner mixture onto the substrate. Addition of crystalline resin to a toner otherwise containing only amorphous resins leads to sharper toner melting and generally lower fusing temperatures. Therefore, toners containing both amorphous and crystalline resins provide energy-efficient printing by allowing low fuser power consumption in comparison to toners comprising exclusively amorphous resins. According to convention, it was thought that the plasticization effect of the crystalline resin occurs only when the crystalline resin is incorporated into the amorphous resin during fusing.
Toner particles comprising a crystalline resin typically comprise from about 5 to 20% crystalline resin. Further increasing the content of crystalline resin generally provides a correspondingly lower fusing temperature. However, increasing the amount of crystalline resin may result in lower charge maintainability and RH sensitivity. In fact, poor charge maintainability and/or toner charge, especially in humid environments, may be observed in the toner particles comprising more than about 15% crystalline resin because of the low resistivity of the crystalline resin within the toner particles. Thus, decreasing the MFT for toner particles by further increasing the amount of crystalline resin therein may cause the toner particles to exhibit a sharp decrease in charge maintainability and/or toner charge.
Even when a shell made from an amorphous resin is formed around a crystalline resin-containing core, a portion of the crystalline resin may migrate into the shell or to the surface of the toner particles if the crystalline resin content is increased. Additionally, during coalescence of the toner particles, the crystalline component may diffuse or compatibilize with the shell resin. Thus, the toner particles having a core-shell structure may still have a surface that includes crystalline resin. As a result, the low resistivity of the crystalline resin that may be present in the shell or at the surface of the toner particles may cause the toner particles to continue to exhibit poor charge maintainability and/or charge, as detailed above.
Thus, a need exists for methods to incorporate a higher amount of crystalline resin into toner particles while avoiding problems associated with the inclusion of the large amounts of crystalline resin.